The objective of the present study is to modify the release of dipyridamole (DIP); which
has a pH dependant solubility in order to overcome its irregular and incomplete absorption
from the gastrointestinal tract. This was achieved by incorporation of a dissolution retarder
such as cellulose acetate phthalate CAP and a dissolution enhancer such as cyclodextrins;
(dimethyl beta cyclodextrin DM-βCD and hydroxypropyl betacyclodextrin HP-βCD). This was
an effective mean of moderating the drastic dissolution behaviour of that basic drug at acidic
pH. Coevaporates of DIP with DM-βCD and DIP with HP-βCD in 1:2 molar ratio were
prepared, followed by coating of these coevaporates by an enteric polymer (cellulose acetate
phthalate, CAP) in 1: 3 drug : polymer weight ratio. In vitro release study was performed for
capsules containing the modified granules at pH values of 1.3, 5 and 6.8. It was found that the
drug release from the modified granules was decreased in a simulated gastric fluid and was
enhanced in a simulated intestinal fluid and reached up to 100%. This could be attributed to the
protecting effect of CAP for the drug granules in the acidic medium, followed by dissolving of
CAP coat in the intestinal fluids which lead the drug to be released easily from the granules.